IDK, what is ideal on the fuel sync... I never had to mess with mine.

I thought you yanked the MSD out of the picture...??? I say take as much variables out as you can until it's figured out, go back to the stock gap on the plugs as well.

when I had a pinging issue with the MSD, it turned out to be weak spark from the worn cap & rotor.

 

I took the MSD out of the loop and tried it on stock, still got the same ping.

Then I re-introduced 1 part of the system each time to see it it was the culprit.
Stock pinged, MSD coil pinged, but no worse, 6A box made no difference either.
hell, I even tested the resistance on plug wires to make sure it wasn't too high and replace the cap, rotor, and plugs just to be sure. I went colder on the plugs and it still didn't help.

 

Sorry to hear the diagnosis has been tough like that

You might consider spraying
Chrysler Combustion Chamber Cleaner in one cylinder only at a time,
let it soak for 30 minutes,
then do a WOT test run
to ID a particular cylinder that is pinging
because of carbon deposits

other options are

to use a 'noid light' in place of an injector,
but this leans the air/fuel at part throttle runs
although not at WOT

use a 'fires in oil' spark plug extension on one cylinder at a time

temporarily use
'ash-less synthetic two cycle oil'
for a test run
the best 30 weight 2 cycle oil
is much more detonation resistant than regular 4 cycle motor oil.

if the pinging goes away with 2 cycle oil
that is a strong indication that there is oil getting by
rings
or
intake valve stem seals
in one or more cylinders

if we had 'bailout' level funds
we could buy one of those
NGK spark plugs that has a tiny pressure sensor built in next to the gap
and could fix the source of the problem quickly

Just call Sec. of the US Treasury Henry Paulson
and say this is a Citibank company vehicle.
They were given $328 Billion this morning.

Isn't that enough to make every active member of DodgeForum a Billionaire?

 

I can't remember; did you pull out the sct tune and see if you could get it to ping? i had a ping issue that after looking at all that stuff unfortunately traced back to the tuner.

 

I did pull the tune and the ping stopped. but that only tells me it really is pinging I'm dealing with, as the stock tune sure as hell better not ping with 93 octane. The SCT 87 octane tune won't ping under any throttle conditions on the 93 octane either.

The thing is, it just sort of "happened" suddenly one day. There wasn't a new tune that I could blame on the ping. It just suddenly started pinging like something internal changed. I was running great on the 93 octane tune for over a month before it happened.

The timing chain was replaced at 75K or so. It's a Cloyes HD double roller chain set at 0* retard/advance. I kind of doubt it's stretched and slipped at 10K. Plus the engine won't ping cold, like first thing in the morning or after it's set a while. It will ping after it's warmed up. I'm trying to figure out what could be affected by a hot engine.

Would a bad cat heating up clog more hot than cold?
Bad O2 sensor lean it out too much? not reading O2's until it hits closed loop, right?
Cylinder head crack between valve seats spreads open when it heats up and cause predetonation?
An exhaust leak wouldn't cause a ping would it? Just wondering if a leak in the headers at the y pipe connection might do something like that.

Not getting any CEL's at all.

 

Yea an exhaust leak could cause a ping sound, but I would think that it would be more like a rattle sound. Is your exhaust welded or clamped?

 

the bit about a cyl head crack occurring
and then opening up with heat
... unfortunately might be the case
but let us hope not

a sudden onset of pinging
most often is due to
intermittent misfire in one cylinder
where the cyl pings because on the next firing
the fill of air/fuel is about 20% higher
because the normally remaining 20% exhaust gas
has been replaced with 20% unburned mixture
and you have 100% VE (volumetric efficiency)
rather than 80% VE

 

Hank,

Do you think that 93 octane on a 87 octane tune would resist predetonation if it were a physical manifestation such as a cracked head? the A/F charge is is leaking regardless, right?

Is it possible the timing is retarded enough on the 87 tune to avoid piston to valve slapping even if the cylinder is getting overloaded with an air/fuel mixture?

 

hmmm, obviously it is complicated

pre-ignition happens regardless of octane
if higher octane fuel
or retarded ignition timing
makes the pinging go away
... then you can definitely say that
IT WAS NOT pre-ignition caused
like the glowing red hot edge of a sharp crack in metal
or carbon deposits too close to a heat source like the exhaust valve

if higher octane fuel
DOES MAKE THE PINGING STOP
then it is most likely a:

too advanced ignition timing for most vulnerable cylinder
compression ratio growth due to deposits
air/fuel mixture change
coolant temperature in cylinder head passage
too high intake air temperature

type of problem

 

Too advanced timing could be an issue, although it wasn't a month ago as far as the SCT tune is concerned

Hopefully a tankful of Techron Concentrate Plus followed by a tank of mopar fuel injection cleaner, followed by a run of MCCC would take care of deposits. The heads on the intake runner side looked clean when I had the intake manifold off.

not sure what might have caused an A/F change other than a bad change in the O2 sensor readings. I can try new sensors.

I'm probably due for a cooling system flush anyway. The cooler 180* t stat seemed to help a bit so maybe that's it.

maybe a switch back to the stock air box instead of the round air cleaner would be a good test as well. Perhaps the IAT could use a cleaning as well.